Manufacturers of internal combustion engines typically provide specifications indicating rated (target) power and/or torque outputs of the various manufactured engines over some specified engine speed range or ranges. At least for engines used in medium and heavy duty applications, such specifications are commonly provided as graphs or plots of engine output torque (wherein engine output torque is engine output power divided by engine speed) versus engine speed. An example of one such graph for a known Cummins M11 engine is illustrated in FIG. 1, wherein engine output torque 5 (in Newton-Meters) is plotted over an engine speed range of between 1100 and 1800 RPM.
Within the medium and heavy duty industry, one of the most common complaints from owners of such vehicles is low engine power. Heretofore, a typical technique for investigating such complaints utilized a known fault tree search technique to check all known possible causes of a low engine power condition. However, such a technique does not provide any way to determine or otherwise estimate the actual output power of the suspect engine. In cases where no cause for low engine power is found, the fault tree search techniques can, at best, provide an indication that the engine should have the rated power.
In another known prior art engine diagnostic method, a disabling action is derived from the engine at a rate proportional to the speed of the engine crankshaft and in a definite phase relation thereto, this disabling action being used to cause (by electronic means) any desired cylinder or cylinders or the engine to become inoperative. By selectively rendering any desired cylinder inoperative while the engine is still running, and without affecting the operation of the other cylinders, an analysis of the resulting engine performance enables ready determination of the relative power contribution of any particular cylinder. Fluctuations in the relative power of any particular cylinder may be caused by, for example, faulty air and/or fuel supply to the cylinder, leakage of combustion gases past the piston rings, etc. While this prior art method is capable of comparing the performance of one cylinder to any other cylinder within the engine, it also suffers from the drawback of not yielding a measure of the total engine output power which may be compared to the engine's rated power.
What is therefore needed is a system and method for diagnosing engine output power that quickly and efficiently narrows down possible causes for low engine power and further provides a simple and efficient technique for estimating actual engine output power over a desired engine speed range for comparison with rated engine output power specifications. Such a system would increase repair efficiency by reducing mis-diagnosis of engine output power related problems and by minimizing unnecessary parts replacement. The present invention is directed toward meeting this need.